In process of natural sucking the calf strikes the udder with its head, what affects milk ejection. To determine the intensity of mechanical calf's influence on the udder a new coefficient was introduced expressing relation between the number of calf head-strikes against the udder and sucking time. In lowland black and white calves the toss frequency was about 2/min. The calculation results can be usable in developing methods to massage cow udders during milking.